Low current-low voltage ignitor



.13111.12, 1943, E. G. F. ARNoTT LOW CURRENT-'LOW VOLTAGEl IGNITOR Filed April 24, 1941 @M51 ,mm

ATTORNEY Patented Jan. 12, 1943 LOW CURRENT-'LOW VOLTAGE `ICrNITOR Edward G. F. Arnott, Montclair, N. J., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 24, 1941, Serial No. 390,060

15 Claims.

My invention relates to electrode structure and especially to the starting electrode for a mercury pool device.

An object of my invention is to reduce the voltage necessary for starting a mercury pool device.

Another object of my invention is to reduce the current applied to a starting electrode of the mercury pool type of discharge device.

A still further object of my invention is to provide a type of starting electrode which will have constant characteristics in regard to Voltage and current in quantity production.

A still further object of my invention is to -provide a starting electrode for partial immersion in a mercury pool which will have substantially constant starting characteristics regardless of variation in the depth of immersion in said pool.

A still further object of my invention is to provide a starting electrode for partial immersion in a mercury pool and which will have little or no variations in starting characteristics due to variations in inactive times.

Other objects and advantages Voi" the invention will be apparent from the following description and drawing in which:

Fig. 1 is an enlarged View of a preferred emv bodiment of my starting electrode with portions broken away to illustrate the interior structure. Fig. 2 is a cross section on lines II-II of Fig. 1.

Fig. 3 is an elevational View of a mercury pool discharge incorporating a preferred embodiment of my invention.

My invention .relates to the starting electrode for mercury pool devices and in its specic form my invention is a substitute for the high resistance make-alive or ignitor electrodes now utilizedr in ignitrons. Ignitrons are constructed with either a glass or metal casing having a mercury pool in the bottom portion thereof and an anode, generally of carbon, above the surface of the mercury. A high resistance material such as boron carbide is partially immersed in the mercury pool. This boron carbide is generally in the form of a conical tip and the discharge is started by applying a suitable current and voltthe starting characteristics because of the more I or less path of `high resistance material which the starting current has to traverse. The installation of the starting electrode in one tube may vary in its vdepth of immersion from another tube and thus cause a difference in starting characteristics between otherwise apparently identical tubes.

When the ignitors of these tubes are in constant use, the boron carbide will reduce its resistance under the influence of the current and heat of operation. Because of the long path through the boron carbide, this change in resistance will noticeably affect the starting characteristics from that condition of the boron carbide When `it has been cooled from a long period ol inactivity. In other words, the characteristics of the boron carbide starter change, depending upon whether the starter is in constant or long intermittent use. Generally, a starter Which has been inactive Vfor a long period may require 200 or 250 peak volts for satisfactory starting operation.

My invention overcomes all these disadvantages of the present ignitor by utilizing a structure with a substantially constant thin layer of high resistance material, regardless of variation in depth of mercury. Because of the short path through the high resistance material, both the voltage and current requirements are Very much less and the period of inactivity does not materially change these operating characteristics.

In Fig. l I have disclosed a preferred embodiment of my invention of `a starting 'electrode l0 which comprises a mass of insulating material Il which may be of ceramic material or other suitable insulating material, and this insulating material may be one of the commercial artificially formed and fired products or a natural insulator such as lava. For convenience in manufacturing, this mass may be in the form of a short rod. I provide, preferably on the cylindrical surface l2 of this rod, depressions preferably in the form of continuous grooves I3. These grooves i3 extend from a top portion it around the cylindrical surface to a portion I5 near the lower edge It of .the rod. The diameter of this rod may be very small, such as of an inch. In these grooves I wind a very ne Wire Il preferably of tungsten and of such small diameter that this Wire will t into the very bottom portion of the groove. 9 mil Wire has proven very satisfactory. The upper end of the Wire preferably wraps around a larger diameter Wire I8,and this `larger 4diameter wire is Wrapped .into the upper -grooves'wlflch willinot be immersed in the mercury pool. This wire I8 has preferably an upward extending portion I9 which may be attached to any suitable starting lead-in connection 2i) disclosed in Fig. 3. The wire l1 resting in the very bottom of the grooves is embedded therein by a coating of high resistance material 2| lling the grooves, so that the cylindrical surface of the insulator is substantially covered with this high resistance material. The composition of this high resistance material may be any one of those disclosed in the copending application of Robert F. Rennie, Serial No. 284,574, nled July 15, 1939, for Ignitron starters. The preferred material is that utilizing one part of silicon carbide with one part of boron carbide mixed together with a small amount of free silicon therein to help bind the material to the insulator Il. This free silicon is anywhere from one hundredth to and the rest boron carbide and silicon carbide. The percentage of free silicon is just suffieient to add strength without adding any undesired characteristic to the coating. Mixtures of 90 to 50% boron carbide and 10 to 50% boron nitride might be used with the silicon. This high resistance material is then covered with a, coating of crystalline powder 22, preferably 60 mesh silicon carbide, in order to reduce the contact resistance with the mercury. This coating is also a sturdy outer rough coating of higher resistivity. The electrode is then placed in the furnace and the resistance material sintered into place imbedding the conductor wire il in the bottom of the grooves. The starting electrode is then immersed to the depth of a few of its grooves in a mercury pool cathode 23 disclosed in Fig. 3. This figure illustrates a glass casing 24, but a metal casing may likewise be used with proper insulation for the electrode leads. The lead of the starting electrode 20 is sealed through the glass casing and the carbon anode 25 is then sealed in place above the mercury pool.

It will be noted that the high resistance material has a very short path from the surface of the electrode 22 to the conducting wire l1. This short path requires a lower voltage and current for starting the discharge. The wire I1 has, of course, a very low voltage drop and brings the current very close to the surface of the mercury with the very thin coating of high resistance material therebetween. This short path through the high resistance material reduces to only a small amount, the useless current owing into the mercury below its surface. As the mercury moves up and down due to the agitation of the pool, the distance between the surface and the conductor wire il will still be substantially constant across the high resistance material and the path therethrough will not change in distance like it would when the mercury is agitated along the surface of a pointed boron carbide starting electrode. Because of the constant thickness of high resistance material between pool and metal conductor l1, the characteristics of the tube will not change with the agitation of the mercury pool. Furthermore, because of the thinness of the coating, a variation in temperature of the coating will not materially affect its resistance such as is appreciably present in the long high resistance path in the boron carbide type of starting electrode.

The electrode obviously can be manufactured very cheaply in comparison with the expensive manufacture of the boron carbide type of electrode. It is also apparent that many modifications may be made in this preferred embodiment,

and accordingly I desire only such limitations to be imposed on my invention as are necessitated by the spirit and scope of the following claims.

I claim:

1. An electrode structure having an end portion for contact purposes, said structure comprising a mass of insulating material having depressions therein extending from a point outside of to a point within the region of said end portion, a conductor in said depressions and likewise extending from a point outside of to a point within the region of said end portion, and a coating of high resistance material imbedding said conductor in said depressions.

2. An electrode structure having an end portion for contact purposes, said structure comprising a mass of insulating material having a continuous groove in its surface extending from a point outside of to a point within the region of said end portion, a wire in said groove partly in the region of said end portion and partly outside thereof, and a coating of high resistance material imbedding said conductor in said groove.

3. An electrode structure having an end portion for contact purposes, said structure comprising a mass of insulating material having depressions therein in part outside of and in part extending into the region of said end portion, a conductor in said depressions of the end region and continuing in said depressions in the part thereof outside the end region, a coating of high resistance material imbedding said conductor in said depressions, and a crystalline powder on the surface of said coating of high resistance material.

4. An electrode structure having an end portion for contact purposes, said structure comprising a mass of insulating material having a continuous groove in its surface extending in to the region of said end portion, a wire in said groove and partly in said end region and partly outside thereof, a coating of high resistance material imbedding said conductor in said groove, and a crystalline powder on the surface of said coating of high resistance material.

5. An electrode structure having an end portion for contact purposes, said structure comprising a mass of insulating material having a groove in its surface extending into the region of said end portion, a wire located in the bottom portion of said groove, a conductor connected to one end of said wire, and a high resistance material covering the other end of said wire to a constant depth in said groove.

6. An electrode structure having an end portion for contact purposes, said structure comprising a mass of insulating material having a groove in its surface extending into the region of said end portion, a wire located in the bottom portion of said groove, a conductor connected to one end of said wire, a high resistance material covering the other end of said wire to a constant depth in said groove, and a crystalline powder on the surface of said high resistance material.

'7. An electrode structure having an end portion for contact purposes, said structure comprising a cylinder of insulating material, a continuous spiral groove in the cylindrical surface of said material extending into the region of said end portion, a wire in the bottom of said groove, and a coating of high resistance material embedding said wire in said groove.

8. An electrode structure having an end portion for contact purposes, said structure comprising a cylinder of insulating material, a continuous spiral groove in the cylindrical surface of said material extending into the region of said end portion, a wire in the bottom of said groove, and a coating of high resistance material embedding said wire in said groove and a coating of crystalline powder on said high resistance material.

9. An electrode structure having an end portion for Contact purposes, said structure comprising a cylinder of insulating material, a continuous spiral groove in the cylindrical surface of said material extending into the region of said end portion, a wire in the bottom of said groove, and a coating of high resistance material embedding said wire in said groove and a coating of silicon carbide on said high resistance material.

10. A discharge device comprising an anode, a mercury pool cathode and a starting electrode having a portion partially immersed in said mercury pool, said immersed portion comprising a. mass of insulation material having depressions therein, a conductor in said depressions and a coating of high resistance material embedding said conductor where it is immersed in said mercury.

11. A discharge device comprising an anode, a mercury pool cathode and a starting electrode having a portion immersed in said mercury pool, said immersed portion comprising a mass of insulating material having a continuous groove in its surface, a wire in said groove extending above the surface of said mercury and a coating of high resistance material between said wire and said mercury pool.

12. A discharge device comprising an anode, a mercury pool cathode and a starting electrode having a portion immersed in said mercury pool, said immersed portion comprising a mass of insulating material having a continuous groove in its surface, a wire in said groove extending Aabove the surface of said mercury and a coating of high resistance material of constant thickness between said wire and said mercury pool.

13. A discharge device comprising an ano-de, a mercury pool cathode and a starting electrode having a portion immersed in said mercury pool, said immersed portion comprising a mass of insulating material having a continuous groove in its surface, a Wire in said groove extending above the surface of said mercury and a coating of high resistance material between said wire and said mercury pool, and a coating of crystalline powder on the surface of said high resistance material.

14. A discharge device comprising an anode, a mercury pool cathode and a starting electrode having a portion immersed in said pool, said starting electrode comprising a cylinder of insulating material, a continuous spiral groove in the cylindrical surface of said material extending above and below the surface of said mercury, a wire in the bottom of said groove extending above and below the surface of said mercury and a coating of high resistance material between said wire and said mercury pool where said starting electrode is immersed in said pool.

15. A discharge device comprising an anode, la mercury pool cathode and a starting electrode having a portion immersed in said pool, said starting electrode comprising a cylinder of insulating material, a continuous spiral groove in the cylindrical surface of said material extending above and below the surface of said mercury, a wire in the bottom of said groove extending above and below the surface of said mercury and a coating of high resistance material of constant thickness between said wire and said mercury pool where said starting electrode is irnmersed in said pool.

EDWARD G'. F. ,ARNOTI 

